Using a Polymorphic VLIW Processor to Improve Schedulability and Performance for Mixed-criticality Systems

Abstract

As embedded systems are faced with ever more demanding workloads and more tasks are being consolidated onto a smaller number of microcontrollers, system designers are faced with opposing requirements of increasing performance while retaining real-time analyzability. For example, one can think of the following performance-enhancing techniques: caches, branch prediction, out-of-order (OoO) superscalar processing, simultaneous multi-threading (SMT). Clearly, there is a need for a platform that can deliver high performance for non-critical tasks and full analyzability and predictability for critical tasks (mixed-criticality systems). In this paper, we demonstrate how a polymorphic VLIW processor can satisfy these seemingly contradicting goals by allowing a schedule to dynamically, i.e., at run-time, distribute the computing resources to one or multiple threads. The core provides full performance isolation between threads and can keep multiple task contexts in hardware (virtual processors, similar to SMT) between which it can switch with minimal penalty (a pipeline flush). In this work, we show that this dynamic platform can improve performance over current predictable processors (by a factor of 5 on average using the highest performing configuration), and provides schedulability that is on par with an earlier study that explored the concept of creating a dynamic processor based on a superscalar architecture. Furthermore, we measured a 15% improvement in schedulability over a heterogeneous multi-core platform with an equal number of datapaths. Finally, our VHDL design and tools (including compiler, simulator, libraries etc.) are available for download for the academic community.